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A composite porous wick with spherical–dendritic powders is proposed, in which the dendritic powders fill the gap between the spherical powders. A unique biporous structure can be realized in this composite porous wick, including small pores between dendritic powders, small pores between spherical and dendritic powders and large pores between spherical powders. Two metal powders (copper and nickel) with two structures (spherical and dendritic) are chosen as the prepared materials, and four composite porous wicks are fabricated. The hydraulic and thermal characteristics of the composite porous wick are studied experimentally. Two capillary pumping stages have been observed in the composite porous wick. And the combination of powders with different metal materials or different structures reduces the effective thermal conductivity of porous wick. Two evaporation heat transfer modes have been observed in evaporation heat transfer experiment, including the evaporation in the vapor grooves and the meniscus evaporation in porous wick. The composite porous wick with dendritic copper powders shows good evaporation heat transfer performance, in which the effective thermal conductivity is not the lowest. Both higher local thermal conductivity and larger equivalent pore diameter exist in this composite porous wick, which is advantage to the meniscus evaporation.

A composite porous wick with spherical-dendritic powders is proposed in this paper. Both the small pores between the dendritic powders and the pores between the spherical and dendritic powders are formed. Moreover, the inhomogeneous local thermal conductivity may increase the tortuosity of the evaporating interface and provide more evaporating area. Two kinds of materials (copper and nickel) and two kinds of structures (spherical and dendritic powders) are chosen to prepare four composite porous wicks, and the evaporation heat transfer characteristics are studied experimentally. Two evaporation heat transfer modes have been observed. The composite porous wick with spherical-dendritic copper powders has the largest critical heat flux of 15.1 W/cm2. At high heat load, the upper surface temperature of composite porous wick may be equal to or even lower than the vapor temperature. The temperature fluctuation may occur, but not affect the evaporator wall temperature. According to the distribution of the evaporating meniscus in porous wick, the critical heat flux may be predicted. The reasonable design of the pore size distribution and large evaporating rate in small pores can increase the critical heat flux.

Accurate prediction and control of the steel plate temperature in the laminar cooling process are very challenging. In this research, an experimental platform was built to measure the heat transfer characteristics of the steel plate in the process of matrix laminar spray cooling when the steel plate is one millimeter away from the upper surface. The “buried couple method” was used, including the cooling temperature and cooling rate. Then, the temperature and the integrated heat transfer coefficient at the steel plate surface were calculated by the time-sequential function method (TSFM). The obtained results show that the fast cooling stage under the water cooling condition occurred in the first 1.5 s, and the measuring point temperature decreased by 8%. The “re-reddening” phenomenon of the steel plate appeared with time, and the measuring point temperature increased by 37%. Second, the maximum calculated difference between the surface temperature and the measuring point temperature was 0.75 °C, and the integrated heat transfer coefficient conformed to the periodic boundary features. The comprehensive convective heat transfer coefficient on the surface was in agreement with the periodic boundary characteristics, and its value exhibited oscillatory attenuation with the cooling process, and the oscillatory peak period was about 6 seconds. Two methods, sequential function method (SFM) and finite difference method (FDM), were used to verify the correctness of TSFM.